Date of Award

2015

Document Type

Open Access Thesis

Department

Marine Science

First Advisor

Ryan Rykaczewski

Abstract

Coastal ecosystems have been subject to increasing stressors over recent decades due to coastal development, human population growth, and climate change. Improving scientific understanding of the environmental factors which influence the productivity of fish populations in coastal ecosystems is vital to their prudent management, especially as the potential influence of anthropogenic climate change grows. Estuaries serve as critical habitats for many fishes of primary ecological, economic, and recreational importance. One such fish, the planktivorous Bay Anchovy (Anchoa mitchilli), is abundant along the Atlantic and Gulf coasts of the US and is a key prey resource for many estuarine and coastal piscivores. Within North Inlet-Winyah Bay estuary Georgetown, SC, the bay anchovy historically was one of the most abundant fishes in the system. However, recent surveys have suggested their populations have declined over the past 30 years. To determine what has contributed to the interannual variability in the fish’s abundance, I used a suite of long-term data sets collected between 1981 and 2002 including biweekly collections of anchovy larvae, mesozooplankton including a calanoid copepod (Acartia tonsa), and chlorophyll-a (Chl-a) concentration as well as monthly river discharge. Here I explored how variability in the timing of life events (phenology) of A. mitchilli’s prey (as measured by copepod density) influenced interannual variability in larval abundance. I also tested how differences between A. mitchilli and copepod phenology could contribute to variability in A. mitchilli larval abundance. The influence of freshwater discharge on the interannual variability of A. mitchilli larval abundance was also explored.

I hypothesized that lower discharge rates could lead to decreased nutrient supply and therefore contribute to declines in Chl-a concentrations and copepod abundances, which would have negative influences on A. mitchilli larval abundance. Analysis revealed that river discharge and A. mitchilli larval density were inversely correlated, contradictory to what was hypothesized. Lack of significant relationship between copepods and A. mitchilli larval density may suggest that copepods are not a significant source of food for larval and adult bay anchovy within the system. Future work is required to fully assess the factors which contribute to the interannual variability in A. mitchilli larval density.

Rights

© 2015, Steven B. Vega Jr.

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